To obtain good flow measurement accuracy and repeatability in large line sizes, a single point flow sensor will most likely not provide an effective solution. This is because, in most cases, large line sizes do not have a sufficient straight run available and may have elbows, blockages, dampers, valves, etc. close to the desired flow sensor location. This results in the desired sensor location being susceptible to swirl and inconsistent, skewed or otherwise distorted flow profiles. Flow rates can be significantly different in different locations across the pipe or duct.
So, what is the solution? One best-practices solution is the use of thermal flow meters in a multipoint configuration.
This is a system where multiple thermal mass flow sensors are installed in the pipe or duct and all the flow sensor points are averaged to achieve accurate and repeatable results. Multipoint systems use between two and eight flow sensor points depending on the size and flow conditions. The thermal flow meter sense points are typically placed at the centroid of equal area cross sections of the pipe or duct. Multipoint thermal mass flow meters also offer three distinct advantages over other large pipe solutions: 1) There are no orifices, moving parts or glass windows to clog or foul; 2) Turndowns of 100:1 are typical and up to 1000:1 available; 3) Sensors are installed in the same plane and can be more easily installed and maintained in large stack, platform-accessed installations.
Fluid Components International has been providing multipoint flow meter solutions for more than three decades and offer three models to best fit the application conditions. Model ST102A is a two point system typically used in line sizes 1 m2
] or less. Models MT100M and MT100S are available in configurations from two to eight points and are used for pipes, ducts and stacks up to 10 m [33 ft]. These flow meters are available to interface with virtually any DCS, PLC or SCADA system with multiple 4-20 mA analog outputs and HART, Foundation Fieldbus, Modbus, or PROFIBUS digital bus I/O options. They also feature best-in-class graphical LCD readouts, EPA CEMS compliance and temperature service up to 450°C [850°F]
MT100 Series Mass Flow Meters
ST100 Mass Flow Meters
FCI Introduces Next-Gen MT100 Air/Gas Flow Meters For Large Diameter Pipes, Stacks and Ducts
Selecting a Flowmeter for Stack Gas Flow Measurement
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Engineering and Calibration Lab Manager
Fluid Components International